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The pipeline industry is undergoing changes because of revisions to safety regulations. These changes include developing standards, recommended practices, and guidelines that can be used by operators to develop, implement, and validate pipeline-integrity verification programs. Methods for verifying pipeline integrity include pressure testing, in-line inspection (ILI), and others, such as a method called Direct Assessment (DA). Each of these techniques has capabilities and limitations that need to be considered in developing and validating a pipeline integrity management program.

In the USA, the US Department of Transportation (DOT) Office of Pipeline Safety (OPS) is changing pipeline safety regulations. These changes affect approximately 160,000 miles of hazardous liquid pipelines and 330,000 miles of natural gas transmission pipelines in high-consequence areas (HCA). The new regulations are intended to decrease the number pipeline failures affecting public safety and the environment. The final rule for hazardous liquids pipelines, dated Jan. 16, 2002, requires that all operators of hazardous liquid pipelines develop and implement integrity management programs including integrity verification of all pipeline segments within an HCA. A similar rule for gas transmission pipeline operators is expected in December of 2003. Since it is expected that the gas rule will contain provisions for use of Direct Assessment, NACE is in the process of developing a series of technical consensus standards guiding implementation of the approach.

The definition of an HCA is complex. For hazardous liquid pipelines, it includes unusually (environmentally) sensitive areas, highly populated areas, and commercially navigable waterways. The final rule for gas pipelines is expected to include proximity to populated areas (including buildings such as schools and hospitals).

What is Inline Inspection?

In-line inspection (ILI) tools, sometimes called pigs, are devices containing sensors designed to scan the pipe wall for defects. There is a wide range in type of tool and the defects they can detect. A wider range of technologies are available to liquid operators than gas operators. The interpretation of signals is complicated, and the level of accuracy depends on the type of tool, how it is run, and the type of defect. There are many advantages and disadvantage to ILI. However, ILI is considered impractical for many pipelines because the tools require construction of a launcher and receiver at the ends of an unobstructed pipe segment without changes in pipe size or bends.

What is Hydrotesting?

Hydrotesting is a method where a pipeline is taken out of service, filled with water, and pressurized to a value greater than the operating pressure. Any defects in the pipe wall that are near failure in a pipeline result in a release of water. Hydrotesting is most often used for new pipelines (or those returned to service) to ensure that construction defects are found. There are many advantages and disadvantage to hydrotesting. However, hydrotesting is not practical for many pipelines because the service interruption is not acceptable (e.g., a single pipeline feeding gas to a city or power plant).

What is Direct Assessment?

Direct Assessment (DA) methods are processes to assess the condition of pipelines with respect to external corrosion (EC), internal corrosion (IC), and stress corrosion cracking (SCC). Each of the DA methods uses techniques to determine the most likely locations for corrosion. These locations are excavated and directly assessed. If these locations most likely to have suffered corrosion are not a threat to pipeline integrity, the remaining section of pipe less likely to have suffered corrosion is considered to also not be a threat.

ECDA is defined by NACE Standard RP0502-02. ICDA and SDDCA standards are under development. The use of DA is expected to improve the overall safety, integrity, and reliability of the pipeline infrastructure because it will allow assessment of pipelines for which other integrity verification methods are not practical. There are many advantages and disadvantages to DA, and there will be some pipelines for which DA is not appropriate.